Spa Choice 472-3-1001 Metal Free Stain Remover for Spas, 1-Pint Metal Free is a sequestering agent that prevents metal staining and corrosion in your spa or hot tub Metal Free also prevents scale build-up Spa Choice Metal Free keeps iron and other metals from oxidizing, which can cause staining to the spa's finish Downloadable User Guide Available Under Product Information: Technical Specifications